---name: web-performance-auditdescription: Web performance audits with Core Web Vitals, bottleneck identification, optimization recommendations. Use for page load times, performance reviews, UX optimization, or encountering LCP, FID, CLS issues, resource blocking, render delays.license: MIT---

Web Performance Audit

Conduct comprehensive performance audits and implement optimizations.

Core Web Vitals Targets

Metric	Good	Needs Improvement	Poor
LCP (Largest Contentful Paint)	<2.5s	2.5-4s	>4s
FID (First Input Delay)	<100ms	100-300ms	>300ms
CLS (Cumulative Layout Shift)	<0.1	0.1-0.25	>0.25
INP (Interaction to Next Paint)	<200ms	200-500ms	>500ms

Performance Measurement

// Using web-vitals library
import { getCLS, getFID, getLCP, getTTFB } from 'web-vitals';

function sendToAnalytics({ name, value, id }) {
  console.log({ name, value, id });
}

getCLS(sendToAnalytics);
getFID(sendToAnalytics);
getLCP(sendToAnalytics);
getTTFB(sendToAnalytics);

Lighthouse Automation

const lighthouse = require('lighthouse');
const chromeLauncher = require('chrome-launcher');

async function runAudit(url) {
  const chrome = await chromeLauncher.launch({ chromeFlags: ['--headless'] });
  const result = await lighthouse(url, {
    port: chrome.port,
    onlyCategories: ['performance']
  });

  await chrome.kill();
  return result.lhr;
}

Optimization Strategies

Quick Wins (1-2 days)

• Enable gzip/brotli compression
• Minify CSS/JS
• Defer non-critical scripts
• Optimize images (WebP, lazy loading)

Medium Effort (1-2 weeks)

• Implement code splitting
• Add service worker caching
• Preload critical resources
• Eliminate render-blocking resources

Long-term (1-3 months)

• Architecture improvements
• CDN optimization
• Database query optimization

Performance Budget

{
  "timings": [
    { "metric": "first-contentful-paint", "budget": 1500 },
    { "metric": "largest-contentful-paint", "budget": 2500 }
  ],
  "resourceSizes": [
    { "resourceType": "script", "budget": 150 },
    { "resourceType": "image", "budget": 300 }
  ]
}

Audit Checklist

• Measure baseline Core Web Vitals
• Run Lighthouse audit (mobile & desktop)
• Analyze real user metrics (RUM)
• Identify largest contentful element
• Check for layout shifts
• Review JavaScript bundle size
• Test on slow 3G connection
• Set performance budget
• Configure monitoring alerts